Basic aluminum compounds, particularly aluminum chlorhydroxides, are conventionally prepared by dissolving aluminum powders, grits, chips or bars in heated solutions of aluminum chloride or hydrochloric acid. U.S. Pat. No. 2,196,016 discloses an example of such a process. Other variations of this process are disclosed for example in U.S. Pat. Nos. 3,891,745; 4,944,933; 3,953,584; 3,957,556; 3,904,741 and 3,873,686.
However, such conventional processes for the preparation of basic aluminum compounds are known to produce a large percentage of high molecular weight species. When analyzed by size exclusion chromatography, in particular high pressure liquid chromotography (HPLC), such compounds are characterized as having a high Band I percent aluminum value. Generally, basic aluminum compounds comprising a high percentage of high molecular weight species are disadvantageous, as they demonstrate relatively lower antiperspirant efficacy than products containing a relatively higher percentage of lower molecular weight species.
Accordingly, various methods have been proposed to prepare so-called "activated" basic aluminum compounds having low amounts of high molecular weight species and which, when analyzed by size exclusion chromatography, demonstrate high Band II and Band III values. Examples of such methods are disclosed in U.S. Pat. Nos. 4,359,456 and 4,859,446; European patent Nos. 0 006 739; and 0 183 171; and European published applications Nos 0 191 628; 0 256 831; 0 274 252 and 0 285 282.
The use of ultrasonic energy to activate and/or otherwise improve chemical reactions is generally known in the chemical arts. For example, U.S. Pat. No. 4,466,870 discloses a method of promoting chemical changes comprising subjecting chemical reactants to ultrasonic energy as a treatment step. Several specific reactions are disclosed for the production of organic compounds in which ultrasonic energy is used to accelerate the disclosed reaction. U.S. Pat. No. 3,346,472 describes a method of manufacturing chemical components, particularly polymeric foams, comprising controlling the chemical reaction and/or polymerization with the use of sonic or supersonic frequencies. In this method, the chemical mixture is passed into contact with first and second vibrating walls during the reaction.
Moreover, U.S. Pat. No. 3,630,866 discloses the improvement of chemical reactions, particularly intra-molecular reactions, by subjecting fluid reactants to ultrasonic energy. Japanese Patent 38-6862 broadly discloses the concept of activating aluminum through the application of ultrasonic energy. This reference requires the sonication of aluminum in an inert, non-aqueous medium or in vacuo. U.S. Pat. No. 1,939,712 teaches activation of metal surfaces by ultrasound treatment for purposes of surface hardening, nitriding, cementation, etc.
However, none of these references discloses or suggests the use of ultrasonic energy to prepare basic aluminum compounds having low amounts of high molecular weight species and a majority of low molecular weight species.